Radio frequency (RF) transmitters of the type used in mobile wireless telephones (also known as cellular telephones) and other portable radio transceivers commonly include transmit power control circuitry that adjusts the power of the transmitted RF signal. The power control circuitry can adjust a power amplifier to increase or decrease the transmitted RF power. Adjusting transmitted RF power is useful for several purposes. For example, in many types of cellular telecommunications systems, it is useful for transmitted RF power to be higher when the transceiver (also referred to as a handset) is farther from the nearest base station and lower when the transceiver is closer to the nearest base station. Also, in some types of multi-mode (e.g., dual-mode) transceivers, such as those that are capable of operating in accordance with both the GSM (Global System for Mobile telecommunication) standard and EDGE (Enhanced Data rates for GSM Evolution) standard, requirements for transmitted RF power differ depending on whether the transceiver is operating in GSM mode or EDGE mode. Similarly, requirements for transmitted RF power can differ in multi-band (e.g., dual-band) transceivers, such as those that are capable of operating in both a GSM “low band” frequency band and a GSM “high band” frequency band. To accommodate different power amplification requirements for multiple bands, the power amplifier system of the transceiver may correspondingly include multiple power amplifiers.
At least some of the above-referenced transmit power control circuitry is commonly located on an integrated circuit chip or die other than that on which the one or more power amplifiers are located. For example, while the power amplifiers may be located on a chip that is part of a stand-alone or dedicated power amplifier module, the portion of the transmit power control circuitry that generates the gain, bias or other power control signals to be provided as inputs to the power amplifiers may be embodied in processing logic (e.g., of a programmed processor chip) and other circuitry that is part of a baseband circuitry module or a mixed-signal circuitry module. In a complex transmitter, such as a multi-mode, multi-band transmitter having several power amplifiers, there can be a significant number of electrical connections or signal lines that convey the power control signals from the power control circuitry to the power amplifier module. For a number of reasons, it is desirable to minimize the number of such power control signal lines.